Electrolyte stratification develops in storage batteries, in particular in lead-acid batteries, which are subject to extreme cyclic operation. This occurs to a great extent in particular when the batteries are discharged to a very low level.
In a stratified electrochemical storage battery, electrolyte stratification causes the total capacity of an unstratified storage battery (without electrolyte stratification) to no longer be available.
Modern automotive batteries are also very frequently operated in low states of charge, which cause electrolyte stratification. In luxury vehicles, loads are still active when the vehicle is not running (no-load current of the vehicle) and/or are activated by the driver (auxiliary heating, seat adjustment, TV, etc.). Electrolyte stratification has a very marked effect on the availability of these comfort loads in luxury vehicles. They must be turned off earlier to guarantee preferred functions such as starting the vehicle.
Electrolyte stratification cannot be eliminated completely. However, stratification is greatly decreased by a very high charge, e.g., at 16 V over a very long period of time in the case of a 12 V battery. During vehicle operation, the battery is usually charged at a low voltage (max. 14.7 V) but the battery is discharged to a low level in top-of-the-line vehicles. Raising the charging voltage to 16 V and/or optimizing the charging procedure to reduce the resulting electrolyte stratification is often associated only with an unwanted intervention in the energy management of the vehicle. In such vehicles, the battery is never fully charged, so stratification is not eliminated.
German Patent Application No. DE 101 06 508 A1 describes a method for estimating the efficiency of a storage battery, taking into account electrolyte stratification, from the battery terminal voltage, battery current, and battery temperature. To do so, an internal voltage drop in the battery due to density differences in the battery acid, a no-load voltage, and an internal resistance are estimated and the efficiency is determined by using a model describing the battery.